1. Field of the Invention
The present invention relates to a rotor of an internal permanent magnet synchronous motor which can rotate at a high speed and to an internal permanent magnet synchronous motor.
2. Description of the Related Art
An internal permanent magnet synchronous motor is known, which provides a plurality of magnet holding holes in the circumferential direction of a substantially cylindrically shaped rotor core and which embeds permanent magnets in the magnet holding holes so as to form a rotor. For example, in the electric motor which is described in Japanese Patent Publication No. 3533209 (JP3533209B), each magnet holding hole is formed by mutually facing straight shaped outside and inside walls, end walls which extend from the ends of the outer wall in the circumferential direction, and passage walls which connect the end walls and the inside wall. Further, a magnet is buried between the outside wall and inside wall. Gaps are formed at the both sides of the magnet in the circumferential direction (inside diameter sides of end walls). Furthermore, the outer circumferential surface of the rotor core at the outsides of the end walls in the diametrical direction is provided with recessed parts parallel to the end walls. Between the end walls and the recessed parts, bridge parts of constant thickness in the diametrical direction are formed.
The rotor described in JP3533209B has thin bridge parts of constant thicknesses at the outsides of the gaps in the diametrical direction. The cross-sectional shape of the rotor core rapidly changes at the both ends of the end walls in the circumferential direction. For this reason, stress concentrates at the both ends of the end walls of the rotor core, and thus when making the rotor turn, the centrifugal force is liable to cause the thin bridge parts to break.